When I use the first server.document-root ("/var/www/htdocs-lighttpd"), it works. However, the second one, which is on a hard drive with more space, does not work. I have copied the "www/htdocs-lighttpd" directory from "/var/" to "/media/Extra/", and ensured that the ownership and permissions are the same:

I'm pretty sure I cloned the permissions that were in the original directories of /var/www/, and nothing else was changed besides the location of the server.document-root within lighttpd.conf, so I'm not sure how the server.username could be an issue.